152 TRANSACTIONS OF THE [MAR. 17, 
gerina. At the present day these genera have left their remains 
most freely in deposits which lie under a depth of oceanic waters 
of 1000 to 2000 fathoms. Their remains are most abundant in 
Assise 2, though they occur also in Assise 3. 
This fauna is distinguished from that of Olenellus by two 
marked features. It is more primitive and also more pelagic. 
The way in which the trilobites are bound together by the single 
feature of a continuous eyelobe shows a unity of origin and a 
closer relationship than is found in the trilobites of any other 
fauna, and yet among these trilobites there are forms which in 
other respects are parallel to the types which developed in the 
later faunas. Thus in Protolenus we have the flat pleurz, with 
diagonal furrow of Paradoxides, but in sub-gen. Bergeronia the 
deeply grooved, geniculated pleurz of Ptychoparia, and at the 
same time the prominent glabella and deep dorsal furrows of 
Solenopleura. Micmacca, as has already been said, predicates 
Zacanthoides of a later fauna. Finally, Protagraulos, in its 
almost obliterated glabella and flat cephaiic shield recalls 
Agraulos and Holocephalina of the Paradoxides fauna. 
It is a more pelagic fauna than that of Olenellus, for we 
notice the absence of many forms of the Olenellus Fauna that 
were differentiated for shore-conditions. Trilobites with fixed 
outer cheeks like Olenellus and Microdiscus are absent ; calca- 
reous corals and sponges are rare, and no Lamellibranch is 
known. On the other hand, Foraminifera are quite common in 
some layers, and the Gasteropods are mostly such as were 
adapted for comparatively deep water. 
If then this fauna-is not that of Olenellus, but one that is 
more primitive and more pelagic, should we look for Olenellus 
above or. below Protolenus? It is to be noted that there re- 
main several Assises near the base of the St. John group which 
have not yielded a fauna of trilobites, so that there are still 
possibilities of the recovery of this genus from these Cambrian 
rocks. In the first assise of Band 6. only an imperfect Ellip- 
socephalus has been found, but some of the Brachiopods of this 
assise are identical with those of the Olenellus Zone. However, 
the crustaceans so far recovered from this assise show no special 
resemblance to those of the Olenellus Zone. 
A consideration in this connection is that the two faunas may 
have been cotemporary, but. incapable of existing in the same 
area, owing to their being adapted to different conditions of 
depth and temperature. If, for instance, the Protolenus Fauna 
was fitted for deeper and more tranquil waters than that of 
Olenellus, we would expect that at a locality where the two 
faunas occurred in succession in a series of deposits, the Olenel- 
